How to use the paperwork-backend.paperwork_backend.common.export.dummy_export_progress_cb function in paperwork-backend

    def save(self, target_path, progress_cb=dummy_export_progress_cb):
        target_path = self.doc.fs.safe(target_path)
        progress_cb(0, 1)
        self.doc.fs.copy(self.pdfpath, target_path)
        progress_cb(1, 1)
        return target_path

def save(self, target_path, progress_cb=dummy_export_progress_cb):
        target_path = self.fs.safe(target_path)
        progress_cb(0, len(self.exporters))
        for (idx, exporter) in enumerate(self.exporters):
            progress_cb(idx, len(self.exporters))
            doc = exporter.doc
            filename = "{}.pdf".format(doc.docid)
            filepath = self.fs.join(target_path, filename)
            exporter.save(filepath, dummy_export_progress_cb)
        progress_cb(len(self.exporters), len(self.exporters))
        return target_path

    def save(self, target_path, progress_cb=dummy_export_progress_cb):
        return self.__save(target_path, (0, self.doc.nb_pages), progress_cb)

    def __save(self, target_path, pages, progress_cb=dummy_export_progress_cb):
        # XXX(Jflesch): This is a problem. It will fails if someone tries
        # to export to a non-local directory. We should use
        # cairo_pdf_surface_create_for_stream()
        target_path = self.doc.fs.unsafe(target_path)

        pdf_surface = cairo.PDFSurface(target_path,
                                       self.__page_format[0],
                                       self.__page_format[1])
        pdf_context = cairo.Context(pdf_surface)

        pages = [self.doc.pages[x] for x in range(pages[0], pages[1])]
        for page_idx, page in enumerate(pages):
            progress_cb(page_idx, len(pages))
            img = page.img
            if (img.size[0] < img.size[1]):
                (x, y) = (min(self.__page_format[0], self.__page_format[1]),

    def save(self, target_path, progress_cb=dummy_export_progress_cb):
        target_path = self.page.fs.safe(target_path)

        progress_cb(0, 4)

        # the user gives us a quality between 0 and 100
        # but PIL expects a quality between 1 and 75
        quality = int(float(self.__quality) / 100.0 * 74.0) + 1
        # We also adjust the size of the image
        resize_factor = float(self.__quality) / 100.0

        img = self.page.img
        img.load()
        progress_cb(1, 4)

        new_size = (int(resize_factor * img.size[0]),
                    int(resize_factor * img.size[1]))

    def save(self, target_path, progress_cb=dummy_export_progress_cb):
        target_path = self.fs.safe(target_path)
        progress_cb(0, len(self.exporters))
        for (idx, exporter) in enumerate(self.exporters):
            progress_cb(idx, len(self.exporters))
            doc = exporter.doc
            filename = "{}.pdf".format(doc.docid)
            filepath = self.fs.join(target_path, filename)
            exporter.save(filepath, dummy_export_progress_cb)
        progress_cb(len(self.exporters), len(self.exporters))
        return target_path